In response to concerns about water quality degradation, communities have constructed wastewater and sewage treatment systems. These treatment facilities discharge water of greatly improved quality, but create a solid waste material in the form of sewage sludge. The sludge may be substantially dried by a sludge dewatering press or other means to leave a moist, soil-like residue that is termed “Biosolids” by the U.S. Environmental Protection Agency. Other potential sources of residue similar to sewer sludge Biosolids are food processing facilities where the residue of food production matter is reduced to sludge, and livestock operations where the animal waste is processed to sludge.
In general, Biosolids are nutrient-rich organic residual solids. When properly treated and processed, Biosolids can be recycled and applied as agricultural fertilizer and in other land applications. Environmental regulations set the criteria for use of Biosolids in such land applications, dependant in large part upon the amount and type of pathogen reduction accomplished by the sewage treatment.
Not all municipal sewage facilities are able to accomplish the level of treatment required to produce a Biosolid for use as a fertilizer or in other high level land applications. In addition, some facilities may only be able to achieve the requisite treatment under normal or below normal conditions, but not able to do so under peak loading or abnormal conditions. Sewage treatment usually involves, among other stages, a primary treatment of filtering suspended solids from the influent wastewater and a secondary treatment of decomposing the organic solids by predatory microbes to destroy fecal coliforms and other pathogens. The facilities may not be adequately equipped to remove toxic metals and other hazardous organics that may be present in the wastewater. This frequently presents a problem in communities where stormwater sewers are combined with the sanitary sewers. These combined sewers collect storm runoff conveying additional contaminants, such as solid debris, chemicals and pesticides that enter the sewer treatment system. Contaminants that are not decomposed by predatory microbes or removed in some other step are retained in the Biosolids. In addition, the increased volume of water runoff may overburden the microbe decomposition capacity. Either condition can produce Biosolids that do not meet the criteria for use as fertilizer. The facilities must then contract with properly licensed haulers to have the Biosolids removed to another treatment facility for incineration or other special handling.
It is known to use liquid ammonia as a solvent and washing agent to separate heavy metals and other organic toxins from soil-like substrates. For, example, U.S. Pat. No. 6,049,021 to Getman, et al. discloses methods for separating toxins and heavy metals from various substrates in a pressure vessel using liquid ammonia or another nitrogenous base to wash the contaminants from the carrier material. It is also known that ammonia is effective in destroying microorganisms. While ammonia and other nitrogenous compounds are usually reduced from wastewater at sewage plant, in a preliminary treatment before microbial decomposition to reduce the oxygen demand, ammonia could be used in a post-dewatering process for additional pathogen reduction.
It is also known to use thermal stripping by hot air injection and vapor recovery to reduce volatile contaminants from soil. A mobile apparatus and method for doing this in-situ is disclosed in U.S. Pat. Nos. 5,631,160 and 5,830,752 respectively.
Accordingly, there is a need in many instances for sewage facilities to have additional methods and equipment to treat Biosolids in order to meet criteria for land applications and use as agricultural fertilizer. It would be useful to have methods using the same equipment be able to effectively treat the Biosolids for the elimination of hazardous material, such as heavy metals, PCBs, pesticides, volatile organics and other toxins in addition to reducing pathogenic microorganisms. It would further be useful to have the same equipment be able to effectively treat other contaminated substrates such as sludge, sediment, soil or debris contaminated with toxic materials in addition to treating Biosolids.